In the second example, we consider a spectral method [1]}, [2]}, [3]}, [4]} with applications in signal estimation and exploratory data analysis. Let \(\xi \)  be an unknown vector in \(\mathbb {R}^n\)  and \(\left\lbrace a_i\right\rbrace _{1 \le i \le m}\)  a set of sensing vectors. We seek to estimate \(\xi \)  from a number of generalized linear measurements \(\left\lbrace y_i = f(a_i^{\hspace{-0.83328pt}\mathsf {T}}\xi )\right\rbrace _{1 \le i \le m}\) , where \(f(\cdot )\)  is some function modeling the acquisition process. The spectral method works as follows. Let
\(D\overset{\text{def}}{=}\frac{1}{m} A\operatorname{diag}\left\lbrace y_1, \ldots , y_m\right\rbrace  A^{\hspace{-0.83328pt}\mathsf {T}},\) 
